1. Field of the Invention
The present invention relates to a conversion apparatus and an imaging system.
2. Description of the Related Art
In recent years, the size of liquid crystal display panels has been increasing. The liquid crystal display panels contain switching elements such as thin film transistors (herein TFTs) fabricated on an insulating substrate. The manufacturing technology has been applied to large screen area sensors (conversion apparatuses) with conversion elements such as photoelectric conversion elements and switching elements and has been in practical use in fields such as radiation imaging apparatuses. The area sensor contains pixels arranged in a matrix and each pixel has a switching element and a conversion element. The representative conversion elements are: conversion elements which convert light from the arranged wavelength conversion layer, which converts radiation such as X-rays into light such as visible light into electric charges, and conversion elements with a semiconductor material which directly convert radiation into electric signals.
The conversion apparatuses used as radiation imaging apparatuses have evolved to have high-sensitivity conversion elements and high driving speed. High-sensitivity conversion elements can be achieved by increasing the area of the conversion elements. Thus, expansion of the area occupied by the conversion element in a pixel (corresponding to an aperture ratio) is required. In order to reduce the noise of the readout signal coming from the conversion element, it is necessary to increase the line width of signal lines and reduce the resistivity thereof. In order to increase the driving speed, it is necessary to increase the size of the switching elements. Further, it is necessary to increase the line width of the gate lines in order to reduce the line resistivity. Accordingly, there is a need to increase the aperture ratio of the pixel, the line width and the size of the conversion element such that high sensitivity and high speed are achieved.
Japanese Patent Laid-Open No. 2002-343952 discloses arranging an interlayer dielectric film between a gate line of a switching element and a lower electrode of a conversion element, and between the gate line of the switching element and a gate electrode of the switching element. This enables increasing the space between the gate line of the switching element and the conversion element, and increasing the aperture ratio by increasing the size of the conversion element in a pixel.
However, Japanese Patent Laid-Open No. 2002-343952 discloses arranging the same interlayer dielectric film between a gate line of a switching element and a lower electrode of a conversion element, and between the gate line of the switching element and a gate electrode of the switching element. Therefore, the characteristic of each element cannot be improved by individually designing the film thicknesses of the insulating film of the switching element and that of the conversion element.